Story: Life in hot springs

Page 1 – Extremophiles

Because of their high temperatures, hot springs have
traditionally been regarded as devoid of life. Research
during the last few decades has, however, shown that they are
teeming with microbes – tiny survivors known as
extremophiles.

Characteristics of extremophiles

Extremophiles are organisms that live in extreme
conditions of temperature, acidity, salinity, pressure, or
toxin concentration.

Most extremophiles are single-celled micro-organisms
belonging to two domains of life – bacteria and archaea.
These differ from fungi, plants, animals and other
single-celled organisms because their genetic material is
dispersed through the cell rather than being enclosed within
a nucleus.

Types of extremophile

The main types of extremophile found in geothermal areas
include:

thermophiles (heat-loving)

acidophiles (acid-loving)

thermoacidophiles (heat- and acid-loving).

For an organism to be classified as an extremophile, it
must live its entire life at these unusual conditions. Many
will actually die if conditions are less extreme.

Discovering extremophiles

In 1966 Thomas Brock showed that microscopic organisms
thrived in hot springs at Yellowstone National Park, USA.
Since then extremophiles have been found all over the world,
and their study is one of the rapidly expanding areas of
biological science. Because of its variety of thermal
features, New Zealand is one of the best places to study
these organisms.

Human limits

Normal human body temperature is 37°C, and a comfortable
bath temperature is about 40°C. Hotter than that, things
get unpleasant and we labour to keep our temperature
stable. After five seconds at 60°C, our skin will be
permanently damaged. We are definitely not
thermophiles.

Studying extremophiles

From the genetic makeup of extremophiles, it is
conjectured that the earliest life on earth evolved in a hot
spring or deep-sea thermal vent several billion years ago.
New Zealand’s geothermal environments may represent similar
conditions. It is also possible that geothermal environments
may be similar to the conditions on other planets or moons
and, if life exists in these places, it may resemble the
extremophiles we see on earth.

On a practical level, extremophilic organisms are of
interest because they contain special molecules such as
proteins that are resistant to high temperatures and have
potential applications in biotechnology.

How extremophiles survive

Unlike most organisms that require organic
(carbon-containing) compounds for their energy or can carry
out photosynthesis, some extremophiles can produce energy
from inorganic compounds.

The hot water found in geothermal areas is formed as the
result of heating of groundwater by deep heat sources. Very
hot water is highly corrosive. As it moves through fractures
deep in the earth it can dissolve minerals or convert them to
other minerals.

When the water reaches the surface, it forms hot spring
fluids. These may contain high concentrations of dissolved
chemicals such as chloride, sulfate, sodium, potassium,
bicarbonate and silica. Also present are minor dissolved
chemicals including calcium, iron, aluminium, arsenic,
ammonia, hydrogen and hydrogen sulfide. Some of these provide
the basic energy source and nutrients for a number of
extremophile micro-organisms.